1. Field of the Invention
The invention relates to high power field effect transistors having a multiplicity of gate, source, and drain electrodes. More specifically, the invention relates to high power, high frequency Schottky barrier type field effect transistors fabricated by planar technology. Such transistor devices are used to advantage in microwave signal amplifier and radar applications.
2. Description of the Prior Art
A high power, high frequency field effect transistor (FET) device has long been sought for numerous microwave and radar amplification applications. FET's are preferred over bipolar transistors and the various types of negative resistance amplifying diodes because field effect transistors have an inherently lower noise figure than other devices. Moreover, microwave circulators are not required as for amplifying negative resistance diodes. Also, the impedance levels commonly encountered with field effect transistors are often more convenient in amplifier design than impedances of other devices.
Unlike a bipolar transistor an FET is a majority carrier device. As such, the FET does not operate by carrier emission over a thermally sensitive barrier and thus does not depend upon a conduction mechanism which varies exponentially with temperature. Hence, an FET is not susceptible to thermal runaway as is a bipolar transistor. Because of this conduction mechanism, the FET will operate satisfactorily over a larger range of ambient temperatures and will tolerate a higher absolute temperature than a bipolar device. Furthermore, a higher thermal resistance package may be used with the FET than may be used with the bipolar device.
Some early FET's having a multiplicity of source, drain, and gate electrodes or contacts made connection to one of elements through the bulk of the device. Such arrangements typically gave high feedback capacitances between input and output elements. The resistance of the bulk material also frequently became a limiting factor in determining the frequency response of the device. Such devices often could not be entirely fabricated using planar technology.
It soon became evident that it was desirable to make contact to all three sets of electrodes upon the surface of the device. Devices were constructed using a multiplicity of two of the electrodes and a single one of the third electrode. Various geometric configurations were tried for making contact to these electrodes. However, the total potential of the device was never realized using these geometries as device operation was severely limited by the use of only a single one of one of the three electrodes.